Electrophotographic apparatus

ABSTRACT

In an electrophotographic apparatus including means for forming an electrostatic latent image on an electrophotographic photosensitive member, developing means for developing said latent image on said photosensitive member with a liquid developer containing liquid carrier and charged toner particles to form a toner image and transfer means for transferring said toner image to a copy member, the improvement comprising squeezing means at a squeezing site for squeezing excessive liquid carrier from at least one of said photosensitive member and said copy member and means for establishing at said squeezing site an electric field extending in a direction and having a magnitude to maintain said toner particles of the toner image against the member bearing same.

United States Patent [191 Takahashi Aug. 12, 1975 ELECTROPHOTOGRAPHIC APPARATUS [75] Inventor: Toru Takahashi, Tokyo, Japan [73] Assignee: Canon Kabushiki Kaisha, Tokyo,

Japan [22] Filed: May 11,1973

[21] App]. No.: 359,221

Related US. Application Data [60] Continuation of Ser. No. 179,073, Sept, 9, 1971, abandoned, which is a division of Ser, No. 729,567, May 16, 1968, Pat. No 3,663,219.

[30] Foreign Application Priority Data May 23, 1967 Japan 42-32962 June 29, 1967 Japan 42-56049[U] [52] US. Cl. 355/10; 96/1 LY; 117/37 LE; 1 lS/DlG. 23 [51] Int. Cl... G03g 15/10 [58] Field of Search 355/10, 3 R, 16; 96/1 LY; 117/37 LE; 118/D1G. 23

[56] References Cited UNITED STATES PATENTS 3,155,546 11/1964 Dirks 118/637 Lehmann 117/37 LE Matkan 118/637 X ll/l966 11/1967 5 7 ABSTRACT In an electrophotographic apparatus including means for forming an electrostatic latent image on an electrophotographic photosensitive member, developing means for developing said latent image on said photosensitive member with a liquid developer containing liquid carrier and charged toner particles to form a toner image and transfer means for transferring said toner image to a copy member, the improvement comprising squeezing means at a squeezing site for squeezing excessive liquid carrier from at least one of said photosensitive member and said copy member and means for establishing at said squeezing site an electric field extending in a direction and having a magnitude to maintain said toner particles of the toner image against the member bearing same.

2 Claims, 5 Drawing Figures PATENTED AUG 1 2 I975 SHEET PATENTEDAUBI2I975 3,899,249

SHEET 2 INVENT OR ATTORNEY ELECTROPHOTOGRAPHIC APPARATUS CROSS-REFERENC E TO RELATED APPLICATION This is a continuation of application Ser. No. 179,073 filed Sept. 9, 1971 which, in turn, is a division of U.S. Pat. No. 3,663,219 issued May l6, 1972.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an electrophotographic apparatus, and more particularly, relates to an electrophotographic apparatus having liquid developing, transfer and sqeezing means.

2. Description of the Prior Art Electrophotography was invented by C. F. Carlson in I938. The fundamental principles of C. F. Carlsons process are disclosed in US. Pat. Nos. 2,221,776, 2,297,691, and 2,357,809. In general, C.F. Carlsons process comprises the following, A photosensitive plate prepared by laying a photoconductive insulating layer on a conductive base, is uniformly charged and image light is projected on the photoconductive layer to form a latent image by selectively discharging the above obtained uniform charge, and thereafter the latent image is developed with toner particles of electrically opposite polarity. The image of toner particles or powder is then fixed directly with heat or with solvent, or is transferred onto another member, such as a plain sheet of copy material.

Liquid developing methods for developing an electrostatic charge pattern were invented by Metcalfe et al and are disclosed in US. Pat. Nos. 2,907,674 and 3,032,432. In accordance with this developing method, a photoconductive insulating layer having an electrostatic latent image is contacted, such as by dipping, with a liquid developer having a liquid carrier and charged toner particles to form a toner image, and the toner image is directly fixed to the photosensitive member, or transferred to another member.

There is a drawback with conventional electrophotography which utilizes liquid developers in that the toner image is disturbed when the electrostatic latent image is developed with liquid developer and the visible image thus formed is transferred onto copying material. Specifically, when copying material is closely contacted to the surface of the developed or toner image, most of the liquid carrier remaining on the surface of the photosensitive plate is removed, causing an abrupt flow or pool of the liquid carrier at point of close contact between the copying material and the photosensitive plate. This abrupt flow of liquid carrier disperses or carries along the toner particles and causes the disturbance of the developed image.

Thus, in order to eliminate the disturbance of the developed image caused by the abrupt flow of the liquid carrier, in accordance with one prior art method, a predetermined gap is provided between the surface of the photosensitive plate carrying the developed image, and the copying material, and an electric field is established between the surface of the developed image and copying material. However, this method gives rise to problems which are difficult to overcome from a technical point of view. Specifically, a considerable amount of liquid carrier is deposited on the copying material upon the transfer of the image, in addition to the toner particles, and therefore it is necessary to remove the excessive liquid carrier which adheres on the copying material. A large amount of liquid developer is wasted if the liquid carrier is evaporated by directly drying the same with hot air, such as by using a fan. Furthermore, removal of liquid developer by evaporation is not preferable because of the creation of an undesirable evaporated gas, and because the energy required for drying the liquid developer is remarkably great. These drawbacks, as mentioned above, are inherent in the conventional liquid developing method.

In order to remove the above drawbacks, another prior art method removes excessive liquid developer from the copying material bearing the toner image by passing the copying material through squeezing rollers and then subjecting the residual toner image to hot air drying treatment.

However, when ordinary paper is used as the copying material, the squeezing of the liquid carrier from the toner image also gives rise to an abrupt flow which carries the toner particles of the liquid developer along with the flow or the transfer of the liquid carrier. This abrupt flow undesirably disturbs the developed image since there is no significant electric attraction between the copying paper and the charged toner particles.

SUMMARY OF THE INVENTION The present invention relates to an electrophotographic apparatus including means for forming an electrostatic latent image on an electrophotographic photosensitive member, developing means for developing said latent image on said photosensitive member with a liquid developer containing liquid carrier and charged toner particles, to form a toner image on said photosensitive member and transfer means for transferring said toner image to a copy member, the improvement comprising squeezing means at a squeezing site for squeezing excessive liquid from at least one of said photosensitive member and said copy member and means for establishing at said squeezing site an electric field extending in a direction and having a magnitude to maintain said toner particles of the toner image against the member bearing same, whereby the disturbance of the toner image is prevented, and an excellent reproduced image is obtained.

In other words in the electrophotographic apparatus of the present invention, before the developed image is transferred to copying material, an electric field is given to liquid developer squeezing means at such site in a direction that the toner is pressed onto the photosensitive plate or, after the developed image is transferred, an electric field is applied to the liquid developer squeezing means in a direction that the toner particles are electrically attracted to the copying material.

The means for forming an electrostatic latent image, which can be employed in this invention, are not restricted to the conventional electrostatic latent image forming apparatus, and the techniques which are disclosed in copending and commonly assigned US. Pat. applications Ser. No. 563,899, filed July 8, 1966 and Ser. No. 571,538, filed Aug. 10, 1966, may be employed.

It is therefore an object of this invention to provide a new electrophotographic copying apparatus.

It is a further object of this invention to provide an electrophotographic apparatus in which a liquid developing means for developing an electrostatic latent image characterized in having high speed and precise image formation properties, and a transfer means for transferring the developed image to ordinary or plain copy paper of low cost and easy handling, are advantageously combined wihtout losing the advantages of both of such means.

It is still a futher object of this invention to provide a new and excellent electrophotographic apparatus which includes means for applying an appropriate electric field to the liquid developer squeezing rollers before or after the image transfer process.

The above mentioned and other objects of this invention will be clarified from the detailed description of the preferred embodiments thereof set forth hereinafter and shown in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing an apparatus of the present invention in which the liquid developer is squeezed before the toner image on the photosensitive plate is transferred to copying material;

FIG. 2 is a schematic diagram showing an apparatus of the present invention embodying a photosensitive plate in the form of a drum and in which the liquid developer is squeezed before the toner image on the photosensitive drum is transferred to copying material;

FIG. 3 is a schematic diagram showing an apparatus of the present invention in which the liquid developer is squeezed after the toner image is transferred to copying material;

, FIG. 4 is a side view of an electrophotographic copying device constructed in accordance with the present invention in which the liquid developer is squeezed from the copying material after the toner image is transferred thereto; and

FIG. 5 is a side view of another electrophotographic copying device constructed in accordance with the present invention in which the liquid developer is squeezed from the copying material after the toner image is transferred thereto.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings in detail, FIG. 1 shows a liquid developer squeezing means of an electrophotographic apparatus in accordance with this invention wherein the toner image on the photosensitive member is squeezed from removal of excessive liquid carrier before the toner image is transferred to copying material. First, an electrostatic charge of a predetermined polarity is deposited on a photosensitive plate A having a photoconductive layer 2 overlying a support I. A light image of the original image is then projected onto the photosensitive plate A to form an electrostatic latent image of the original image and thereafter, this latent image is developed by a liquid developing process to form a toner image on the photosensitive member A comprised of liquid carrier 3 and charged toner particles 5.

As shown in FIG. 1, after this liquid development, excessive amounts of carrier liquid 3 remain on the photosensitive member A and, in accordance with this embodiment, is squeezed out before the toner image is transferred to a sheet of copying material 4. Specifically, when the copying material 4 and the photosensitive member A having the toner 5 and the carrier liquid 3 closely contact each other, an electric field in a direction for pressing or retaining the toner particles 5 onto the photosensitive member A, is applied to a liquid de veloper squeezing roller 6. Thus, with this arrange ment, disturbance of the toner image can be prevented even if the carrier liquid 3 is squeezed out when the photosensitive member A and the copying material 4 are closely contacted.

Thereafter, an electric field of polarity opposite to that of the electric charge of the toner 5 is applied to a transfer roller 7 to attract the toner 5 and deposit the same on the copying material 4 as the copying material 4 is separated from the photosensitive member A.

As a means for applying the electric field to the squeezing roller 6 which squeezes out the liquid developer before the toner image is transferred and to the transfer-roller 7, an arrangement may be employed, for example, wherein an electric field of the same polarity as that of the electrostatic charge of the toner 5 is applied to the squeezing roller 6 and an electric field of the opposite polarity to that of the toner 5 is applied to the transfer-roller 7 by means of the electric source E The means for applying the electric field, is not restricted to the above arrangement. For example, one of the liquid developer squeezing rollers may we made of an insulating material and the liquid deveioper may be squeezed while a corona discharge is applied to the roller.

The arrangement shown in FIG. 1 can be operated so that the copying material 4 is brought in close contact with a photosensitive plate A bearing a negative toner image, and the two are then brought into close contact with each other by electroconductive rubber rollers 6 and 7 under a pressure of about g/cm and about l000 V of DC voltage is given to the roller 6, and about +1000 V of DC voltage is applied to the roller 7. Under these conditions it is observed that the image does not flow at all, and the next copying operation can be performed at a copying efficiency of 100% without requiring a cleaning operation.

An excellent result is obtained when this invention is applied to developing the latent image produced by the processes and the photosensitive plates disclosed in US. Pat. applications Ser. Nos. 563,899 and 571,538, mentioned above.

FIG. 2 shows an electrophotographic apparatus employing the combination of an electrophotographic copying drum and a liquid developer squeezing roller 6 and a transfer roller 7. In this device, the photosensitive plate A is in the form of a cylindrical drum which rotates continuously and comprises a photoconductive layer 2 on a support 1.

In operation, the photosensitive plate A is charged by means of corona discharger l0 and image light of the original copy is projected onto the photoconductive layer 2 by using an exposing device 11 whereby an electrostatic latent image of the original image is formed on the photosensitive plate A. The photosensitive plate A is then dipped into a vessel 12 containing liquid developer comprised of a liquid carrier and charged toner particles to develop the latent image.

After the development of the electrostatic latent image, copying material 4 is introduced between the cylindrical photosensitive plate A and a liquid squeezing roller 6 and a transfer roller 7. A voltage of the same polarity as that of the electrostatic charge of the toner image formed on the cylindrical photosensitive plate A is applied to the liquid developer squeezing roller 6 and a voltage of polarity opposite tothat of the electrostatic charge of the toner image is applied to the transfer roller 7 to increase the image transferring effect;

In the operation of the arrangement shown in FIG. 2, when the polarity of the toner particles was adjusted to be negative and a DC voltage of about l() V was applied to the squeezing roller 6 and a DC voltage of about +1000 V was applied to the transfer roller 7, image deterioration was not observed at all. Thereafter a drying operation was carried out by using a hot air drier l7 and an excellent image was obtained.

FIG. 3 shows a liquid developer squeezing means of an electrophotographic apparatus of the present invention wherein excessive liquid carrier deposited on the copying material after toner image transferred, is removed. Specifically, after the toner is transferred onto the copying material 4, a considerable amount of carrier liquid 3 in addition to the toner 5 adheres to the copying material 4. In order to remove the excessive liquid carrier 3, an electric field in a direction in which the toner 5 is electrically attracted to the copying material 4, is applied between liquid developer squeezing rollers 8 and 9 which are operated by any operational means (not shown). Thus, by this arrangement, the disturbance of the toner image caused by the flow of the liquid carrier is prevented.

In regard to the means for applying the electric field between the rollers 8 and 9, an electric source E shown in FIG. 3 can be utilized. Of course, the means for applying the electric field should not be restricted to the above. For example, one of the liquid developer squeezing rollers 8 and 9 may be made of an insulating material and the liquid developer may be squeezed while a corona discharge is applied to this roller.

When an electric field is applied between the liquid developer squeezing rollers 8 and 9, it is necessary to provide at least one means for preventing the rollers 8 and 9 from contacting each other, or for covering either of said rollers 8 and 9 with electrically insulating material or semiconductive material, in order to prevent the liquid developer squeezing rollers 8 and 9 from short-circuiting when the copying material 4 does not pass between the liquid developer squeezing rollers 8 and 9. As shown in FIG. 3, it is possible to insert a resistance R to the voltage applying circuit so as to limit the current and reduce potential short circuit effects.

When the copying material 4 is passed between the squeezing rollers 8 and 9, a voltage from 50 V to 3 kv is applied between the rollers 8 and 9 in such a direction that the toner 5 is electrically attracted to the copying material 4. Thus, the toner particles 5 can be attracted to the copying material 4 by an electric field as the carrier liquid 3 is removed by the squeezing rollers 8 and 9. Therefore, it is possible to produce an excellent transferred image without causing the disturbance of the image.

It is not necessary that two liquid developer squeezing rollers 8 and 9 be provided, rather it is quite possible to replace either of the squeezing rollers 8 or 9 by other additional means for squeezing the liquid developer. For example, one of the liquid developer squeezing rollers 8 and 9 may be replaced by a squeezing means other than a roller.

In FIG. 4, there is shown an electrophotographic apparatus similar to the apparatus shown in FIG. 3. However, in this device, the photosensitive plate A is composed of a cylindrical drum which, in operation, rotates continuously. In operation, the photosensitive plate A comprising a photoconductive layer 2 on a support I is charged by means of the corona discharger l0, and then the image light of the original copy is projected by means of the exposing means 11 to form electrostatic latent image on the photosensitive plate A. Then, the photosensitive plate A is dipped in the vessel 12 containing liquid developer to develop the latent image and form a toner image of the original image. Thereafter, the copying material 4 is laid thereon with a slight distance from the surface of the toner image.

An electric field is applied to the electroconductive roller 7 to transfer the developed visible or toner image to the copying material 4 by making use of the electrophoresis of the toner particles 5 contained in the liquid developer. After image transfer, the copying material 4 is passed through the squeezing rollers 8 and 9 in order to remove the liquid carrier 4 adhered on the copying material 4. As the copying material 4 is passed through the squeezing rollers 8 and 9, a voltage is applied therebetween by means of the electric source E in the direction in which the toner particles 5 are electrically attracted and maintained'on the copying material 4. In other words, when the toner particles 5 are negative, a negative voltage is supplied to the squeezing roller 8, and a positive voltage is supplied to the squeezing roller 9.

As an example of the arrangement shown in FIG. 4, when a voltage from 50 V to 3 kv is applied between the squeezing rollers 8 and 9, the toner particles 5 are attracted to the copying material 4 by means of the electric field and the carrier liquid 3 adhered on the copying material 4 is removed. Therefore, after having dried the same with a hot air drier 17, an excellent image can be obtained without disturbing the image. After transferring the toner image, the photosensitive plate A is cleaned with the cleaning brush l5, and the copying operation can be repeated.

It is not an indispensable factor of this invention that two liquid developer squeezing rollers 8 and 9 be provided, but rather either of them can be replaced by other means for squeezing off the liquid developer. For example, one of the liquid developer squeezing rollers 8 and 9 may be replaced by a squeezing means other than a roller.

FIG. 5 shows an arrangement which is a modification of the electrophotographic apparatus shown in FIG. 4 and is the same as the electrophotographic device of FIG. 4 except that the image transferring roller 7 also operates as the squeezing roller 9.

In the device of FIG. 5, the photosensitive plate A is composed of a continuously rotating cylindrical drum, and the photosensitive plate A comprising a photoconductive layer 2 on a support 1 is charged by means of a corona discharger 10. The light image of the original copy is projected by the exposing means 11 and an electrostatic latent image is formed on the photosensitive plate A. Thereafter, the photosensitive plate A is dipped into the vessel I2 containing liquid developer to develop the latent image while copying material 4 is laid thereon with a slight distance from the surface of the image.

An electric field is applied from the back surface of the copying material 4 through the image transferring electroconductive roller 7 which functions as both a transferring and a squeezing roller, and the visible image is transferred onto the copying material 4 by making use of the electrophoresis of the toner particles contained in the liquid developer.

After transfer of the toner image, in order to remove excessive liquid carrier 3 adhering on the copying material 4, the copying material 4 is passed through the squeezing rollers 8 and the transferring roller 7. As the copying material 4 is passed between the rollers 7 and 8, a voltage is applied to the squeezing roller 8 by means of the electric source E in a direction in which the toner particles 5 are electrically attracted to the copying material 4.

When a voltage from 500 V to 3 kv is applied between the squeezing roller 8 and the image transferring roller 7, the toner particles 5 are attracted by an elec tric field to the copying material 4 and the carrier liquid 3 which is adhered on the copying material 4 is removed, and therefore it is possible to produce an excellent image without disturbing the toner image.

After the completion of the transfer of the toner image, the photosensitive plate A is cleaned by the cleaning brush l5, and the carrying operation can be carried out repeatedly.

As is shown in FIGS. 3 through 5, it is preferable that the copying material 4 should be kept almost horizontal in order to further minimize the disturbance of the torier image caused by the flowing out of the carrier liquid at the region between the transferring roller 7 and the squeezing rollers 8 and 9.

As has been explained hereinabove, this invention provides a new and remarkably effective electrophotographic apparatus having liquid developer squeezing means free from any disturbance of image which is caused by the flowing out of the liquid developer when the liquid developer is squeezed with the conventional liquid developer squeezing rollers.

According to the conventional transfer arrangement, the transferred image is disturbed upon transferring the image on the photosensitive plate to the copying material by closely contacting the copying material to the image. This invention eliminates such disadvantage by squeezing the liquid developer before such transfer while applying an electric field to the squeezing means.

Further, according to a conventional process, the transferred image is disturbed when the image on the photosensitive plate is transferred to the copying material by contacting the image on the photosensitive plate with the copying material, and then the liquid developer is squeezed by the liquid developer squeezing roller. This invention succeeds in removing such disadvantage by squeezing the liquid developer after imagetransfer while applying an electric field to the liquid developer squeezing roller.

In accordance with this invention, the liquid developer can be advantageously effectively used by reusing the liquid carrier removed from the copying material by returning the same through a conduit (not shown) to a storage tank. On the other hand, in accordance with this invention, it is possible to use ordinary paper as the copying material, and the cost of the copying material is low. The structure of the squeezing means in accordance with the liquid developer squeezing arrangement of this invention is very simple and can be produced economically. In addition, it is possible to squeeze out the liquid developer at a high rate of speed and therefore this invention is very useful in electrophotographic copying devices in which liquid developing procedures are adopted.

What is claimed is:

1. An electrophotographic apparatus for reproducing an original image on copy material comprising: means for forming an electrostatic latent image of said original image on an electrophotographic photosensitive member; means for developing said electrostatic latent image with a liquid developer containing a liquid carrier and charged toner particles to form a toner image on said photosensitive member; means for contacting said toner image with said copy material and squeezing said photosensitive member and said copy material to remove excessive amounts of liquid carrier; means for applying an electric field in a direction and having an amplitude to maintain said charged toner particles on the surface of said photosensitive member during said squeezing of said photosensitive member and said copy material; means for thereafter transferring said toner image onto said copy material by contacting said copy material with said photosensitive member and means for applying an electric field which attracts the transferred toner image to the surface of said copy material.

2. An electrophotographic apparatus as in claim 1, wherein said squeezing means includes a freely rotatable electroconductive roller and said means for establishing said electric field includes circuit means connecting said electroconductive roller to a source of electrical potential. 

1. An electrophotographic apparatus for reproducing an original image on copy material comprising: means for forming an electrostatic latent image of said original image on an electrophotographic photosensitive member; means for developing said electrostatic latent image with a liquid developer containing a liquid carrier and charged toner particles to form a toner image on said photosensitive member; means for contacting said toner image with said copy material and squeezing said photosensitive member and said copy material to remove excessive amounts of liquid carrier; means for applying an electric field in a direction and having an amplitude to maintain said charged toner particles on the surface of said photosensitive member during said squeezing of said photosensitive member and said copy material; means for thereafter transferring said toner image onto said copy material by contacting said copy material with said photosensitive member and means for applying an electric field which attracts the transferred toner image to the surface of said copy material.
 2. An electrophotographic apparatus as in claim 1, wherein said squeezing means includes a freely rotatable electroconductive roller and said means for establishing said electric field includes circuit means connecting said electroconductive roller to a source of electrical potential. 